Electronic transition lasers such as rare gas excimer, dimer, and charge transfer lasers offer scalable high energy photon sources in the ultraviolet and visible wavelengths. These new lasers have high efficiencies and can be scaled to high pulsed output energies by increasing the volume, pressure and energy deposition into a high pressure gas mixture contained within the lasers. Rare gas halide electronic transition lasers operate on similar principles. First, an intense source of electron excitation either from an electron beam, a high voltage self-sustained electric discharge, or an electron beam sustained discharge is used to excite mixtures of rare gases plus a small percentage of a molecular additive. A rare gas is a dominant component of the mixture because the electron excitation is initially deposited into ionization and excitation of the rare gas. Operation of these lasers at high total pressures is necessary for their proper operation. Large volume, self-sustained glow discharges have been extremely difficult to achieve at high pressure unless special precautions are taken because high pressure glow discharges rapidly form an instability and convert to an arc discharge. Arc discharges tend to constrict into small streamers thereby eliminating the volume excitation necessary for proper laser operation. For this reason, electron beams have been used as the primary excitation method for rare gas excitation transfer lasers.
Although the electron beam method provides a well controlled and well characterized source of excitation of high pressure gases, it does have serious practical limitations which make self-sustained discharge excitation an useful alternate method. An efficient high pressure electric discharge for electronic transition lasers is characterized by a discharge that is volumetric and stable (i.e., does not degenerate into a constricted arc). The electron energy in the discharge should be high enough to produce sufficient rare gas ions and metastables and have a sufficiently high current density in order to produce a sufficient number of excited rare gas species in a short time period which is less than the time required to react all of the molecular additive. These three criteria require a high voltage, high energy discharge circuit incorporating some method for stabilizing the discharge to prevent arcing.
Many problems have been encountered in the efficient design of discharge circuitry necessary to produce the high electron temperatures required in high pressure rare gas buffered mixtures. Typical problems are that the gas tends to break down at too low a voltage. Also, discharges at electron energies necessary for efficient pumping of the laser tend to constrict into an arc unless the discharge pule has a very steep rate of rise (under 100 nanoseconds) and the duration is kept shorter than the arc formation time or the time to react all the molecular additive. The gas after breakdown has a very low impedance (i.e., less than several ohms) which necessitates a low impedance electric discharge pulse forming circuit for efficient energy deposition into an electric discharge gas laser (EDGL) load. In addition, high voltage and high energy charging circuits (e.g., Marx generators, L-C generators, or transformers) typically have too large an inductance to provide either a rapid voltage rise time or a sufficiently low output impedance for optimum energy transfer to EDGL's. Thus, a key problem associated with these types of lasers is the development of an efficient, long lived, non-destructive, non ablative reliable and inexpensive method of electron energy deposition into the lasers. The pulse rise time shaping, pulse width compression and impedance matching circuitry of the present invention solves the above problems.